On Sat, Jun 01, 2013 at 10:19:11PM -0700, Yitzchak Scott-Thoennes wrote:
> On Sat, Jun 1, 2013 at 10:23 AM, Dirk Koopman <djk at tobit.co.uk> wrote:
> > Quite a lot of other perl artefacts have been deprecated and then removed.
> > Why does this one persist? In what way is it useful or intuitive?
>> Because it is the result of an optimization - lexicals are reset upon leaving
> scope, not entering it, and only if the my() was reached during execution.
>> Nevertheless, I believe Dave Mitchell had a patch to fix it that never
> quite made it in.
The original patch was a proof-of-concept that hoisted the run-time
effects of my to the start of the containing scope. So that from a
run-time point of view,
{
AAA;
my $x = ...;
BBB;
my $y = ...;
CCC;
my $z = ...;
DDD;
}
is executed like
{
my ($x,$y,$y);
AAA;
$x = ...;
BBB;
$y = ...;
CCC;
$z = ...;
DDD;
}
The main problem with it was that in something like the following:
while (<>) {
next unless /rare condition/;
my ($lots, $of, $lexicals) = split;
...
}
all those lexicals would be initialised and cleared every time round the
loop, rather than just on rare occasions: which could be quite a
performance hit.
--
Modern art:
"That's easy, I could have done that!"
"Ah, but you didn't!"